Hey so quick update on this, still haven't been able to move the car.
I had a long chat with my brother in law who's a properly qualified mechanic. He thinks, mostly based on the fact that the clutch pedal is harder to push in now than normal, that it's less likely to be the clutch fluid since if that had leaked the pedal should be super easy to push down with no resistance, and also it comes back up when letting off it it doesn't just stay down on the floor. The leak I saw down my driveway might be incidental, or still could be related, I don't know at this point.
Any thoughts on this? I suggested maybe there's some kind of spring assist that brings the pedal back up, but that doesn't explain why it's stiffer to press down than normal.

I've also spoken to 2 other different mechanics and both of them as well as my bro all agree that regardless whether it's the slave cylinder or something else, it'll probably need the gearbox dropped out to fix and if that's happening anyway then the clutch should be replaced while it's all stripped down- The car has 175000KM (a touch under 110,000 miles) and god only knows if it's even been done before, I didn't get a service history log when I bought the car.

There are 2 slave cylinders available in Aus that we've been able to find (both interstate and would need to be ordered in) but we can't find a single clutch kit available anywhere.

I'm wondering if a clutch kit from the R170 2003 SLK 320 mention earlier would be directly compatible/interchangeable with the Crossfire? Just to make the search a little easier.. I'll take any win I can get at this point